Lubricating oil composition



Patented Oct 17, 11944 2,360,623 LUBBICATING OIL COMPOSITION Raphael Rosen, Elisabeth, N. 3., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application March 1, 1941, Serial No. 381,388

6 Claims. (CL 252-44) This invention relates to improvements in lubrica'ting oil compositions. More particularly, it is concerned with hydrocarbon lubricating oils improved in stability by the addition of a quaternary phosphonium compound.

At the high temperatures of the order of 200 internal combustion engines, the instability of lubricating oils is associated with the susceptibility of these oils to undergo oxidation and thermal decomposition with resultant formation of corrosive substances and objectionable carbonaceous deposits on hot engine parts. As internal combustion engines are being designed and manufactured increasingly for higher power output, the requirements for greater stability in motor lubricants become steadily more stringent.

The main object of the present invention is to provide lubricating oil compositions of improved stability for satisfactory performance in the lubrication of internal combustion engines.

Advantageous efiects on the stability of lubrieating oils of various metallo-organic compounds containing a, metallo-element selected from the second, third, and fifth groups of the periodic table of elements are described in my U. 8. Patents No. 2,181,913, No. 2,181,914, and No. 2,181,915, all granted on December 6, 1939. My copending application, Serial No. 307,263, filed December 2, 1939, now issued as Patent No. 2,265,819 of December 9, 1941, of which the present application is a, continuation-in-part, discloses organophosphorus compounds that are useful for stabilizing lubricating oils.

Among the different types of organo-phosphorus compounds considered for the purpose of improving lubricating oils are the phosphine derivatives of hydrogen phosphide, PI-Is, in which organic radical substituents are directly linked to the phosphorus atom by carbon to phosphorus bonds. In these phosphines, organic radicals may be substituted for any or all of the three hydrogen atoms, giving the primary, secondary, and tertiary phosphines. Investigations have brought to light that while these phosphines, particularly the tertiary phosphines, have some value as antioxidants in stabilizing motor lubricants, they are surpassed in effectiveness by quaternary phosphonium compounds, which may be considered as additive compounds of the tertiary phosphines 0., and higher, encountered in the operation of and organic molecules con ining anegative function, which usually has a halogen, sulfur, nitrogen, or an oxygen constituent.

The phosphonium stabilizing agents, with which the present invention is concerned, have compositions formulated as follows:

[RmPlinX wherein R represents organic groups, i. e., chiefly hydrocarbon radicals selected from the type: alkyl, alkylene, cyclo-alkyl, aryl, alkaryl, and aralkyl; P represents a central quaternary phosphorus constituent in the molecule joined directly to carbon atoms of the R groups; and X repre sents a negative function such as a hydroxyl radical, a negative radical of an organic or inorganic acid, or the like. The subscript n denotes the number of R groups linked to the quaternary phosphorus constituent to satisfy exactly four valence bonds thereof. of course, if the X group is polyvalent, the phosphonium radical [RnP] must be combined insufiicient number, denoted by m, to satisfy the particular valence of X; e. g., if X is a sulfate radical, the generalized formular is lRmPlzx.

In the most readily pro'curable quaternary phosphonium compounds, each organic radical is monovalent, thus making the subscript .n=4, but if the quaternary phosphorus constituent has a double bond linkage to a carbon atom, the subscript n will be less than 4, nevertheless, the compound still belongs to the quaternary phosphonium class of interest provided 4 valence bonds of the phosphorus are directlylinked to carbon atoms.

It is to be understood that. the R groups in the quaternary phosphonium compounds may be dissimilar and may contain substituent atoms, for example, halogen, nitrogen, oxygen, or sulfur, etc., or substituent groups, e. g. hydroxyl, alkoxv, carboxy, keto, amino, mcrcapto, etc. A number of compounds which illustrate these variations are: triphenyl ethyl phosphonium hydroxide and its salts, trimethyl cetyl phosphonium chloride, trimethyl allyl phosphonium naphthenate, phenyl benzyl dibutyl phosphonium dihydrogenphosphate, tricyclohexyl octadecyl phosphonium nitrate, tri (hydroxy-ethyl triamyl phosphonium) phosphite, tetrabenzyl phosphonium sulfate, trimethyl chlorcetyl phosphonium acetate, triphenyl octyl phosphonium hydroxide, and ethylene hexaethyl arsphosphonium bromide.

From extensive experience in using quaternary phosphonium and variousmetallo-organic compounds as lubricating oil additives, I have found that aromatic or aryl groups present among the R groups tend to improve the stability of these compounds and that alkvl groups among the R groups are favorable to the oil solubility of these compounds.

Since the quaternary phosphonium compounds are to be added to the lubricating oils for effecting the stabilization in very small concentrations of substantially less than by weight, and generally as little as 0.01% to 1.0% by weight, they are as a class, adapted to be employed for the present purposes. The solubility of the quaternary phosphonium compounds canv be modified by increasing the length and/or I number of alkyl radicals, or a desired increase in concentration may be obtained with the aid of a solubilizing or dispersing agent. However, certain quaternary phosphonium compounds are pre-eminently suitable on account of their marked eflectiveness and economical manufacture.

The preferred phosphonium compounds for stabilizing lubricating oils are the salts in which the quaternary phosphorus constituent is attached to 4 monovalent hydrocarbon radicals and the negative radical is an acid anion radical.

These compounds are readily prepared and are particularly satisfactory in their stability and solubility characteristics.

At this point, it is desired to explain more fully the nature of the negative function as it exists in the quaternary phosphonium compounds. As a rule, this function is electronegative to both hydrogen and phosphorus and is present generally as an anion in combination with hydrogen in hydro acids, salts, or other ionizable compounds in which hydrogen acts as a cation. Some examples of these negative functions are the halide ion (e. g. Cl", I,-Br), the thiocyanate (SCN-), nitrate (Nor), sulfate (Soa=), hydroxyl (OH phosphite (PO3 bicarbonate (HCOr), acetate (CHaCOO), phenate, carbamate, and phenol sulfide radicals. It is recognized in the science of Chemistry that the atoms of elements and radicals are classifiable according to their degree of electronegativity to oneanother. The elements which are most non-metallic, e. g. the halogens, oxygen, sulfur, and nitrogen, are most electronegative,

for atoms of such elements. and radicals con-- taining them have'highly negative volt electron values as determined from their relative bond energies with other elements.

As previously mentioned, the tertiary phosphines, which are identified as the phosphines containing three carbon to phosphorus bonds or three monovalent hydrocarbon radicals attached to the trivalent phosphorus constituent, are capable of reacting with organic compounds containing a negative function to form quaternary phosphonium salts. These salts have been represented by various types of formulae, one of which is the following:

phosphonium salts as being molecular addition compounds.

The quaternary phosphonium salt formation reaction is represented, also, asfollows:

The tertiary phosphines are adapted for use is an initial material in producing thev quaternary phosphonium salts, because they are capable of combining with the Rx molecules, 1. e. compounds such as alkyl halides and other organic compounds containing negative functions. The tertiary phosphines can be made by well-known methods from Grignard reagents or by other reactions, such as, dialkyl zinc compounds with PCla. Typical examples of the tertiary phosphine compounds are triethyl phosphine, (Cal-I5) 3P, triphenyl phosphine (CcHshP. dibenzyl isoamyl phosphine (caveman-cramp 1 The quaternary phosphonium bases which are represented by [RaPlOH are also highly basic,

being comparable in this respect to the quaternary ammonium bases and even to KOH. Accordingly, the quaternary phosphonium bases, which the phosphonium salts tend to form-by hydrolysis, are readily neutralized by acids to the quaternary phosphonium salts. The quaternary phosphonium bases may be utilized in the present invention, and they first may be converted into salts, if so'deslred. I

-Quaternary phosphonium salts were prepared for use in the present invention by a classical procedure described in an article by Mlchaelis and Soden, Annalen, vol. '229, page 295 (1885). This procedure is exemplified in detail by the preparation of iodide as follows:

A 10 g. sample of triphenyl phosphine was placed in a flask with 20 cc. of ethyl iodide. The mixture was then refluxed on a water 100 C. for a total of 10 hours. The p ct of the reaction was a yellow crystalline solid. Ether was added to the flask and the solidmacerated therein. The solution was then filtered and the The crude product was dissolved in hot alcohol.

filtered, and recrystallized from a mixture of alcohol and water to form colorless plate crystals.

'. The weight of these crystals was 11.7 This refined product made a 73% theoretical yield and had a melting point corresponding closely to the melting point 146-165 C.) reported in the literature for triphenyl ethyl phosphonium iodide, (CsHs)aP(CHa)I.

To determine .the relative merits 'of various compounds as stabilizing agents, in addition to service tests, the following analytical tests were conducted: I

The cone test, which correlates with conditions and results obtained in internal combustion entriphenyl ethyl phosphonium that gines in service, is used to quantitatively ascertain the amount of carbon-like material (in grams) deposited in two hours from a lubricating oil composition allowed to flow at a rate of 30 cc. per hour around a groove in a metal cone of standardized'dimensions while the cone is held at a temperature of 250 C. The cones used are constructed of metals similar to those used in the construction of internal combustion engine parts.

This test indicates what effect the addition agent has in the formation of undesirable carbon-like deposits on hot engine parts.

Representative results from a series of runs on oil compositions are presented in the following example:

. Example Cone test (deposit in Lubricating oil composition rams) Blank oil Blank oil+0.2% triphenyl arsine Blank oil+0.2% triphenyl phosphine Blank oil+ 0.2% triphenyl ethyl phosphonium iodideease From comparative data such as shown inthe above table, it is noted that the quaternary phosphonium salt addition agent acts very efiiciently in minimizing undesirable deposits on the hot metal surfaces.

To evaluate the oxidation inhibiting action of the quaternary phosphonium compounds in lubricating oil blends, the Oxygen Absorption Rate Test, which is a regularly employed standardized test for judging the ability of lubricants to resist oxidation under accelerated oxidation conditions, was used. This test is carried out by bubbling measured amounts of oxygen through the lubricating oil samplemaintained at200 C., the oxygen being continuously recycled. The

' amount of oxygen absorbed per cc. of the oil sample is measured quantitatively at the end of each consecutive minute period. The results are recorded as the number of cc. of oxygen ab-- sorbed per 10 cc. of oil during each 15 minute period. This testis carried out under conditions correlated to service conditions but with intensified action of pure oxygen intimately mixed with the oil. As a general rule, in this accelerated oxidation test the first two periods are the most crucial and indicative of the resistance of the oil. to oxidation. In the first period there is an induction lag which makes the amount of oxygen absorbed relatively low, but in the second period the oxygen absorption reaches a peak or maximum after which the rate of absorption tends to decrease in a regular manner. Thus, it is ascertained from the data for the initial two or three periods how wellthe oil composition resists oxidation.

The samples of the same hydrocarbon lubricating oil (S. A. E. 50) used as a reference, or blank, were added small amounts of various inhibitors to be tested as anti-oxidants and results of the oxidation tests on these samples are illustrated asfollows:

I s Oxidation rate 5 Sample tested g cc. oil/15 min.

Blankoil 103 213 101 B.ankoil+0.2%trlphenylphosphine 68 120 B ank oil+ 0.2% triphenyl ethyl phosphonium 10 Willie 3 23 From the foregoing data on the oxidation rate, it can be observed that the quaternary phosphonium salt is more than three times as efiective as 5 the tertiary phosphine, from which it is derived,

' for retarding oxidation, and consequently considerably more effective for reducing deterioration of lubricating oils in this respect.

It is to be understood that one or more of the 20 quaternary phosphonium compounds, featured by this invention may be used to protect various types of hydrocarbon oils from deterioration by oxidation and thermal decomposition, particularly in motor lubricants, i. e. petroleum hydro- 25 carbon oils having viscosities ranging upwardly from 60 Saybolt seconds at 100 F., i. e. upwardly in S. A. E. number beginning with an S. A. E. 10 lubricating oil. However, the oils to be improved may bemore viscous, as in the case of semi-fluid 0 lubricants or greases, or less viscous. The oils to be used as a base in the lubricants may have high or low viscosity indices, may comprise fatty oils, natural or synthetic oils, bright stocks, or distillates, and may be finished by various refining processes, e. g. acid treating, absorptive clay refining, solvent extraction, selective precipitation, etc.

' Other additives may also be incorporated in the lubricating oil compositions, as for example,

40 agents which aid in solubilizing and stabilizing the phosphonium compound, corrosion inhibitors, oiliness agents, oxidation inhibitors of other types,- dyes, soaps, thickeners, viscosity index improvers, pour point depressors, solvents, sludge dispersers, detergents, etc,

The present invention is not to be .limited to any particular addition agent, nor to any theory as to the effect of these substances, nor to the particular amounts of the addition'agents to be used.

I claim: 1. A motor lubricating oil composition comprising a hydrocarbon lubricating oil and a small amount, sufficient to substantially stabilize said oil against oxidation, of a phosphonium compound having the type formula:

RAPX

wherein Rn represents hydrocarbon radicals chosen to satisfy exactly four valence bonds of the quaternary phosphorus constituent and X represents an anion radical having a valence number represented by m.

2. A lubricant for rubbing metal surfaces come 4.. A lubricant for rubbing metal surfaces comprising a hydrocarbon lubricating 011 containing where R1, R2, R3, and R4 are hydrocarbon radicals and X is an anion.

6. A lubricant for rubbing metal surfaces comprising a hydrocarbon lubricating oil blended with a small amount, sufficient to substantially stabilize said -oil against oxidation, 01' a quaternary phosphonium compound having the formula:

R4 where R1, Ra. Ba, and R4 are hydrocarbon radicals and X is a salt-forming anion.

RAPHAEL ROSEN. 

